From: Tom Lane <tgl@sss.pgh.pa.us>
To: Victor Yegorov <vyegorov@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Estimates on partial index
Date: Thu, 18 Aug 2016 09:56:10 -0400
Message-ID: <766.1471528570@sss.pgh.pa.us> (raw)
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Victor Yegorov <vyegorov@gmail.com> writes:
> Settings:
> random_page_cost 2.5 ¤
> seq_page_cost 1 ¤
> Question is — why IndexScan over partial index is estimated less than
> BitmapHeap + BitmapIndex scan. And how can I tell Planner, that IndexScan
> over 1/3 of table is not a good thing — IndexScan is touching 10x more
> pages and in a typical situation those are cold.
In that case you've got random_page_cost too far down. Values less than
the default of 4 are generally only appropriate if the bulk of your
database stays in RAM.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, vyegorov@gmail.com
Subject: Re: Estimates on partial index
In-Reply-To: <766.1471528570@sss.pgh.pa.us>
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